Brain Stimulation Can Manipulate Dream Content

Source: LMa

While asleep, we interact with our dream bodies in a dreaming world, and movement is one of the most commonly reported dream experiences besides visual imagery. It's striking that we can recreate such vivid bodily experiences in a state when our physical body is completely unresponsive. Research thus far suggests that similar areas of the brain are active during both waking and dreaming body movement. More generally, REM sleep dreaming is characterized by high activity in sensorimotor brain networks.

Recently, a study aimed to investigate whether the sensorimotor cortex underlies the generation of movement and bodily experiences in dreaming. The authors used a method called transcranial direct current stimulation (tDCS) to inhibit activity of the sensorimotor cortex during REM sleep, and observe the effect on bodily sensation and movement in dreams.

In the study, ten participants were recruited to spend two nights in the sleep laboratory: one night with tDCS stimulation applied during REM sleep, and one night with sham-stimulation.

During the night with tDCS, the experimenters applied 1mA electric current to the participants‘ scalp over the sensorimotor cortex during 10 minutes of REM sleep. During the sham-stimulation night, the experimenters similarly placed electrodes on the scalp but simply switched on the tDCS device without applying a current, and this only for 10 seconds at the beginning and end of 10 minutes of REM sleep.

After this 10-minute REM sleep period, participants were awakened in order to report their dreams. This procedure was repeated two to three times per night, depending on a participants' sleep pattern.

When participants were awakened, they were asked to give a verbal dream report and to fill in the Bodily Experiences in Dreams (BED) Questionnaire. This 41-item questionnaire consists of items in 5 general categories of bodily experience: vestibular sensations, tactile experiences, movement, movement alterations, and body schema alterations (e.g., changes in body shape).

Two blind judges also carried out a content analysis of the dream reports and scored whether the report contained any movement of the dream-self, and what type of movements occurred— either single action, repetitive action, or passive movement. For instance, “diving” was classed a single action; “riding a bike downhill” as a passive movement; “writing something” as a repetitive action. A total of 50 dreams were analysed.

After analysing the questionnaire data, the authors found that tDCS condition decreased the proportion of dreams with movement compared to the sham-stimulation, but there were no differences for the other categories of bodily experiences. Basically, participants were less likely to report movement in their dreams after receiving tDCS.

According to the judges' analysis as well, participants in the tDCS condition reported less movement in their dream reports but this was specific to repetitive actions. There were no effects of tDCS on single actions or passive movements in dream reports. The authors suggest that this may be due to the nature of repetitive actions being more reliant on sensorimotor cortex, in that repetitive actions depend on learned memory for motor sequences.

Overall the results support that using electrical stimulation to inhibit sensorimotor cortex activity specifically decreases presence of repetitive actions in REM sleep dreams. This provides novel evidence that the sensorimotor cortex is causal in the generation of dream movement.

Finally, the data also replicated prior findings that movement is very common in dreaming, but that other bodily sensations such as tactile and vestibular sensations are more rare. An interesting avenue for future research will be to explore whether and how such sensations could be modulated by the dreaming brain.